Penguin poo reveals how volcanic eruptions almost killed off the seabirds

Gentoo penguins excreting guano onto the snow near in Potter Cove, King George Island

Stephen Roberts

Ardley Island, in the South Shetland Islands of Antarctica, is inhabited by around 5,000 pairs of gentoo penguins. This makes it one of the largest breeding colonies for the penguin species, yet penguins on the island have had a tough time surviving.

The penguin colony was periodically wiped out by three volcanic eruptions, a study by the British Antarctic Survey has found. By analysing 8,500-year-old biogeochemical traits in sediment from a lake on the island (translation: tracking ancient penguin poop through the ages), the research team was able to see how close the penguins in the region came to extinction.

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Sediment cores were taken from Ardley Lake (above) when it was frozen as this provides a more stable platform for coring

Stephen Roberts

According to the research team, the three eruptions caused penguin chicks to be buried alive under ash and nesting sites to be rendered unusable due to the expulsions. "The biggest response was in relation to three large eruptions 5,300, 4,300, and 3,000 years ago," Roberts explains.

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"We also found that it took surprisingly longer for a colony to fully establish itself or sustainably re-establish itself after the large eruptions". After each eruption, it took the penguin colony around 400-800 years to become sustainable on the island again.

The analysis of the penguin history was completed by looking at penguin guano, found in the island's sediment. Guano is the accumulated excrement of seabirds; based on recent estimates, penguins on the island produce around 84.5g of guano per day and each breeding season around 139 tonnes of the dry mass is produced on the island.

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At its peak, the population of gentoo penguins on the island may have reached an upper limit of around 10,000, charts within the Nature Communications research paper estimate.

"Geochemical analyses of guano signatures in lake sediments can thereby provide long-term records of past penguin presence in their catchments," it says.

Roberts explains that by analysing the percentage of guano in the historic deposits it was possible to estimate the size of the penguin populations in history. "Because we know the percentage of guano in the sediment we can model around the sediment accumulation and the catchment," he says.

Once the team had worked out how much guano was contained within each sediment sample it was possible to tie this to external environmental factors. The periods where penguin guano was seen the least tied in with the times of the volcano eruptions.

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It is now possible for the biogeochemical analysis to be used to investigate how other penguin colonies have developed. "The techniques we've developed in this study could be applied elsewhere in Antarctica to reconstruct past changes in penguin colony sizes and that would provide us with a valuable and long term perspective of modern-day penguin colony changes," Roberts says.

"That would allow us to better assess lots of different places and show us the potential changes in climate and sea ice conditions can have."